Radiology/Contrast CT

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Expert: Michael K. - 8/26/2014

QuestionI had a contrast enhanced Head CT and a non contrast CT (done at different times-3 weeks apart). I'm wondering if the use of contrast medium increases scanning time and radiation dose. Because, when I had the contrast CT I was there longer than the during the CT that didn't have the contrast. These scans were preformed in Canada.

Also, the second CT (with dye) included the temporal bones(using thin slices) to assess the inner ear. They used a 64 slice scanner. Does this mean I had more radiation exposure because the scan included the inner ears?

AnswerKathy,

The use of contrast does not affect the time or the dose. I am not sure what was the difference is time as it takes 2-4 seconds for scans like you are describing to be obtained. The time on the table may have been longer because there are several more steps when the contrast is used. As we inject the contrast into your arm, we do not start the scan right away because the contrast hasn't made it to where we are scanning, ie your head. It takes about 15 seconds to make it to the arteries from the arm. After that we need to wait until the contrast reaches the equilibrium in a phase that we need in the arteries, or veins, or soft tissues (all depending on the question we are answering). So while we wait, you are on the table, but not being scanned. After the correct delay to allow contrast to make it to the right time/place then we scan.

Hope this helps.

Michael

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